Many virulence factors directly influence death pathways in infected hosts to counteract immune responses. In other instances, virulence factors delay cell death to allow sufficient time for pathogen replication, and ultimately induce cell death to aid in spread of the pathogen. This application seeks to define the link between several category A virulence factors and cell death (primarily apoptosis) pathways, and to design mechanism-based strategies to counteract the processes. The proposed Program Project consists of six projects and three supporting cores. In the first project, Dr. Liddington will determine crystal structures of key anthrax virulence complexes, as well as co-crystallize virulence factors in complex with inhibitors derived in the other projects and a Core. In the second project, Dr. Salvesen will determine targets and inhibitors of the Variola serpins. In the third project, Dr. Lipton will explore the neurodegenerative effects of botulinum toxin. In the fourth project, Dr. Reed will explore the function of novel virulence factors predicted by bioinformatics approaches. In the fifth project, Dr. Mustelin will explore the mechanism of cell death induced by Yersinia YopH. In the sixth project, Dr. Pellecchia will design and synthesize small molecules and peptides targeting high priority virulence factors. Two scientific Cores will provide the infrastructure for protein expression, purification and preliminary structural studies and high-throughput inhibitor screening, chemical synthesis and resynthesis of lead compounds. Each project has a discovery theme, and most have an applied component. The elements of the proposed Program Project are highly interdependent, with many complementary aims. The discovery themes range from elucidation of the mode of virulence factors binding to their targets, to the discovery of novel pathogen death regulators, to the design of peptide mimics and small molecules that interact with virulence factors. The applied components in most of the projects aim to discover peptide and small molecules that ablate virulence factor activity. As such, the latter project has a major impact on the applied components since it will produce molecules and strategies for testing in the other projects. Altogether, the information derived from these studies may reveal strategies for preventing or ameliorating cell death induced by pathogenic bacteria, thus complementing traditional antibiotics in the prevention and treatment of bacterial I diseases and agents of biological warfare.